Our hypotheses are that alpha-2 adrenergic mechanisms modulate colonic sensation in health and in patients with irritable bowel syndrome associated with increased frequency of bowel movements and urgency; and that lower doses of the alpha-2 agonist, clonidine, are required to reduce colonic sensation in IBS compared to health; these antinociceptive effects are achieved without altering colonic compliance or motor function in patients with irritable bowel syndrome. The specific aims of the study are to study the alpha-2 adrenergic modulation of colonic compliance, tone and sensation in healthy human volunteers; to study the alpha-2 adrenergic modulation of gastrointestinal and colonic transit time in healthy human volunteers; and to study the alpha-2 adrenergic modulation of colonic transit, tone, compliance, and sensation in patients with well-characterized autonomic function who have irritable bowel syndrome associated with increased frequency of bowel movements and/or urgency.